Creating Arrays

Declaring an Array

We can have an array of ints, strings, doubles, or any of the other types we've seen so far. We can even make arrays of arrays, but that's a topic for later.

An array is stored in a single variable, and unless we're using var to infer the type, we need to state that it's an array and what it's an array of. We can specify an array of some other type by adding a pair of square brackets ([]) after the other type. For example, int[] is an array of integers, and String[] is an array of strings. The following code declares, but does not initialize, several array variables of different types.

int[] arrayOfInts;
String[] arrayOfStrings;
double[] arrayOfDoubles;

Creating a new Array

We'll usually want to initialize an array variable by creating a new array. To create an array, we write the new keyword, the array's type, and the array's size inside the square brackets. For example, new int[10] would create a new array that holds ten integers. We'll modify the previous code to declare and initialize our array variables:

int[] arrayOfInts = new int[10];
String[] arrayOfStrings = new String[5];
double[] arrayOfDoubles = new double[1000];

This has created three arrays: an array of ten integers, an array of five strings, and an array of one-thousand doubles.

A couple of notes about these arrays before we continue:

• Each array's size is fixed once it has been created. We cannot grow or shrink these arrays.
• The arrays are not empty. An array always contains exactly the same number of values. When we create new arrays like this, they are initialized with the default value for their type: 0 for numeric types, false for booleans, and null for strings or other objects/reference types. A value of null means there is no string at that position in the array. We'll learn more about null later, but for now it's enough to understand that it represents the absence of an object.

If we want to create a small array that starts with a specific set of values instead of the default value for its type, then we have another option:

int[] countdown = new int[] { 10, 9, 8, 7, 6, 5, 4, 3, 2, 1 };
String[] names = new String[] { "Alice", "Bob", "Charlie" };

This could be used for larger arrays, but it's not very practical. If our array isn't, we'll probably want to use a loop to set the initial values after we create the array.